Conventional edge-lit backlight modules in mass production employ a light guide panel. Because the light coupling distance between the light source of a backlight module and the light guide panel is required to be accurate, the light guide panel tends to be positioned by rigid positioning column(s) or right-angle positioning rim(s). However, the light source of the backlight module radiates heat while in use, which heats and expands the light guide panel. Because the positioning column or the right-angle positioning rim is made of rigid material and has no buffer action, generally come the following problems: the heat expansion or cold contraction quantity of the light guide panel cannot be fully absorbed, easily causing the warpage and deformation of the light guide panel; and the light guide panel is in rigid contact with the positioning structure, easily causing the light guide panel to fracture when being impacted.